1. Field of the Invention
The present invention relates generally to a therapeutic pulse generator system used to provide energy efficient stimulation/pacing by causing controlled cellular depolarization based on pre-measured charge transfer and is accomplished by periodic electrical characterization of the electrode-tissue interface.
2. Related Art
Material, in the form of edible food and liquids, is directed through the organs in the gastrointestinal (GI) tract via peristaltic movement. The timing of the contractions of each of the organs is controlled by a physiological mechanism. The gastric “slow wave” in the normal human stomach, which regulates the contraction propagation frequency in the stomach, is reported to be approximately three cycles per minute. Other organs in the GI tract normally have different propagation frequencies. For example, it is believed that the frequency at the top of the duodenum is approximately 12.5 cycles/minute, and the frequency more distally in the small bowel, is approximately 9 cycles/minute (cpm).
Abnormalities in myoelectric activity in the GI tract may result in a variety of disorders harmful to human subjects. For example, gastroparesis exists when a patient experiences delayed gastric emptying. Conversely, dumping syndrome and some diarrhea states may be caused by gastric emptying which is too quick. Constipation results when the colon fails to move fecal matter properly. By contrast, chronic dumping syndrome, short bowel syndrome, and idiopathic diarrhea may be the result of the colon moving matter too quickly. Table 1 identifies a number of different clinical conditions which result from irregular gastric and intestinal myoelectric activity.
Pacemakers have been used for many years in cardiac care. These devices are typically implantable, and include control circuitry and electrodes that stimulate the heart tissue on a regimented basis. Pacemakers have been suggested for use in pacing the stomach; however, the level of understanding of stomach pacing is not as well developed as cardiac pacing. In addition, the requirements for effective stomach pacing are quite different from those for cardiac pacing. Ideally, a gastric pacemaker should deliver electrical signals to entrain natural gastric function.
U.S. Pat. No. 5,690,691 to Chen et al discloses a portable or implantable gastric pacemaker includes multiple electrodes that are positionable on the inner or outer surface of an organ in the gastro-intestinal tract and which are individually programmed to deliver a phased electrical stimulation to pace peristaltic movement of material through the GI tract. The pacemaker will accommodate variations in stimulation pulse amplitudes, stimulation pulse durations, stimulation pulse periods, and relative stimulation pulse phasing among the electrodes. Computer control may be used to adjust and vary all stimulation parameters delivered by the electrodes to achieve effective treatment and re-training of an organ for natural pacing. The pacemaker may be programmed with parameters to enhance or accelerate peristaltic movement through the gastric tract or to attenuate the peristaltic movement to treat such conditions eating disorders or diarrhea.
U.S. Pat. No. 3,411,507 to Wingrove discloses a device for gastrointestinal stimulation which uses an electrode positioned on a nasogastric catheter and an electrode secured to the abdominal wall. In operation, the nasogastric catheter is inserted into the patient's stomach. To institute peristaltic activity, the patient is preferably given an electrical stimulation for the first five seconds of every minute until positive results are obtained. The electrical stimulation is for a period of 0.1 milliseconds (ms) every 25 ms of the first five minutes. Wingrove also discloses using electrical stimulation of the same order of magnitude as the normal range of periodicity of the inherent peristaltic pacemaker action of the duodenum. The stimulation process is discontinued after the first bowel movement. Wingrove suffers from the disadvantage of only being a short term device. That is, it is only useful for patients in a hospital setting, and particularly patients that are laying down. Wingrove offers no long term solution to patients with digestive disorders. In addition, Wingrove does not allow for adjusting the electrical stimulation to suit the needs of a particular patient.
U.S. Pat. No. 5,292,344 to Douglas discloses a percutaneously placed electrical gastrointestinal pacemaker which provides for stimulation, sensing, delivery of fluids and nutrients, and pH sensing. The Douglas device may be used to treat a wide variety of gastric disrhythmias and may be used for both short and long term patient care. In operation, a plurality of electrodes are percutaneously and endoscopically placed on the inner lining of the gastrointestinal tract. The electrodes are all simultaneously pulsed with the same current and stimulation pulse rate. The current and stimulation pulse rate are adjustable by both mechanical and electrical systems. A pH sensor and a pressure sensor are connected inside the stomach, and are used for analysis of the electrical stimulation effects. Control circuitry is used in a feedback loop to control the timing of stimulation pulses. For example, if a response to the electrical stimulation is delayed beyond a controllable time threshold, a signal is given to provide another stimulative pulse. In addition, the control circuitry may be used to uniformly adjust the strength of the stimulation pulse, and to alert primary care providers of possible dangers. The Douglas gastric pacemaker provides several advantages. First, it is portable, and may be worn by a patient during day-to-day activities. Second, it allows for long term pacing. Third, it provides multiple electrodes and feedback elements. However, the Douglas system requires intense signals to be delivered to one region of the stomach, and does not address destructive interference problems which may occur when multiple sites are stimulated simultaneously.
Several other U.S. patents show the use of electrical stimulation of organs. For example, U.S. Pat. No. 5,188,104 to Wernicke et al. discloses stimulation of the vagus nerve for the treatment of eating disorders such as compulsive over-eating, bulimia, or anorexia nervosa. Wernicke et al. does not discuss the treatment of gastric motility disorders or the restoration of normal gastric peristalsis. U.S. Pat. No. 5,423,872 to Cigaina discloses stimulating a single electrode pair affixed to the stomach for the purpose of decreasing the frequency of the gastric slow wave. The Cigaina device is used for treating obesity and other over eating disorders. U.S. Pat. No. 4,921,481 to Danis is related to a process for monitoring the frequency of gastric myoelectric signals to aid in the correct placement of gastric feeding tubes. U.S. Pat. No. 5,197,491 to Anderson describes a technique for placing an electrode into a patient's stomach adjacent to the heart for cardiac stimulation. U.S. Pat. Nos. 6,243,607 and 6,449,511 to Mintchev describe gastrointestinal pacemakers with both fixed and variable stimulus. Neither patent correctly references the essential link between entrainment of the gastric slow wave and improvement of gastric motility disorders. None of the aforementioned patents describe the use of energy efficient load characterization and predetermined charge based stimulation technique described herein.